The present invention provides a process for the photopolymerization of vinyl compounds in the presence of a photoinitiator.
Photopolymerization has many useful technical applications as, for example, the curing of lacquers and coatings in the manufacture of printing plates and in letter press printing.
Photopolymerization is also useful in the dental field as well. Photopolymerizable materials are used in the preparation of dental fillings and sealings, of crowns and bridges and artificial teeth and dentures, see, for example, British Pat. No. 569,974, DE-OS No. 31 36 484.5 corresponding to U.S. Ser. No. 413,804 filed Sept. 1, 1982, GB No. 1 428 672, U.S. Pat. Nos. 4,243,578, 4,267,133 and GB No. 2 018 666A.
British Pat. No. 1 408 265 describes photopolymerizable materials which contain as a photoinitiator a mixture of:
(a) at least one photosensitizer of the formula ##STR1## wherein X is CO, C(R.sup.1)(R.sup.2) or C(R.sup.3)(OR.sup.4); R.sup.1, R.sup.2, R.sup.3, R.sup.4, which may be the same or different, are hydrogen or hydrocarbyl groups; n is 0 or 1; and the groups A, which may be the same or different, are hydrocarbyl or substituted hydrocarbyl groups, and wherein the groups A may be further linked together by a direct link or by a divalent hydrocarbyl group, or in which the groups A may form a fused aromatic ring system, the groups A being aromatic or substituted aromatic groups when n is 1 and X is C(R.sup.1)(R.sup.2) and when n is 0, and
(b) at least one reducing agent capable of reducing the photosensitizer when the photosensitizer is in an excited state and having the structure ##STR2## wherein M is an element of Group VB of the Periodic Table and the units R, which may be the same or different, are hydrogen atoms, hydrocarbyl groups, substituted hydrocarbyl groups or groups in which two units R together with the element M form a cyclic ring system, no more than two of the units R being hydrogen atoms or substituted hydrocarbyl groups and wherein element M is attached directly to an aromatic group R, at least one of the other units R has a ##STR3## group attached to M.
British Pat. No. 1 465 897 discloses photopolymerizable materials useful in dentistry which contain as a photoinitiator a mixture of:
(a) at least one photosensitizer of the formula ##STR4## in which the groups A, which may be the same or different, are hydrocarbyl groups or substituted hydrocarbyl groups; and
(b) at least one reducing agent capable of reducing the photosensitizer when the photosensitizer is in an excited state and having the formula ##STR5## wherein M is an element of Group VB of the Periodic Table and the units R, which may be the same or different, are hydrogen atoms, hydrocarbyl groups, substituted hydrocarbyl groups, or groups in which two units R together with the element M form a cyclic ring system, no more than two of the units R being hydrogen atoms and the element M not being attached directly to an aromatic group.
The resulting mixtures can be cured by exposure to visible light or through ultraviolet rays. Examples of the photosensitizers include biacetyl, benzil, p,p'-dialkoxy benzil, benzoin, and camphorquinone. Reducing agents include propylamine, dimethylaminoethyl methacrylate, N,N'-dimethylaniline and piperidine.
European patent application No. 00 49 922 describes the use of N,N'-disubstituted cyclic 1,3-diaza compounds, particularly N,N'-disubstituted imidazolidine and hexahydropyrimidine as an accelerator in materials hardened with ultraviolet light.
German patent application No. P 31 36 484.5 describes a process for the photopolymerization of vinyl compounds in the presence of ketones and cyclic or heterocyclic compounds, particularly 5-substituted barbituric acids which are used as reducing agents.
It is an object of the present invention to provide a method of photopolymerizing vinyl compounds in the presence of a photoinitiator which comprises a carbonyl compound and an accelerator or a reducing agent. The method provides a rapid curing of the vinyl compound by means of irradiation with either ultraviolet light or visible light. The resulting polymers produced according to the present invention have excellent color fastness.